Method of using a catheter for traversing total occlusions

ABSTRACT

A medical device and method for traversing an occlusion in a vessel includes a straightening sleeve positioned at a distal aspect of a catheter, a steering sleeve having an arcuate distal end, and a guidewire disposed through the steering sleeve. The steering sleeve has a first position in which the arcuate distal end is straightened within the straightening sleeve, and a second position in which the steering sleeve extends distally past the straightening sleeve to expose the arcuate distal end. The tip of the arcuate distal end of the steering sleeve or the guidewire can be used to pierce the occlusion. An arrangement of hub assemblies with locking mechanisms and motion limiting structures facilitates adjusting and locking the relative positions of the straightening sleeve, the steering sleeve, and the guidewire. Detent mechanisms are associated with the motion limiting structures for providing controlled incremental movement of the sleeves and the guidewire.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/838,313 filed on Aug. 14, 2007, now U.S. Pat. No. 8,109,953which claims priority of U.S. Provisional Application No. 60/837,899filed on Aug. 14, 2006. The content of these prior applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to catheters and methods oftreating the stenosis of an artery. In particular, the present inventionrelates to catheters and methods for puncturing, crossing and debulkingchronic total occlusions (CTOs) in arteries caused by the buildup ofarterial plaque tissue, and to hub assemblies used with such catheters.

2. Description of the Related Art

Chronic total occlusion (CTO) is a condition where arterial plaquetissue grows to complete stenosis of an artery and prohibits blood flow.A CTO is formed by the agglomeration of three separate physiologicalmaterials: (i) cholesterol or fat, (ii) collagen or fibrous matter, and(iii) calcium-based deposits. A CTO is also often referred to as afunctional occlusion.

There are two causal pathogenic phenomena often associated with theformation of a CTO. The first is the late development of an acuteocclusion. The second is the progressive occlusion of a long-term highdegree stenosis. Both involve a pre-existing plaque or thrombus to whichthe fat and fibrous material adhere, building up until a blockage of theblood vessel occurs.

The CTO mass or CTO body, consisting of fat, fibrous matter, and calciumdeposits, begins to form with fat and fibrous material attaching first.Over time the fat or cholesterol is replaced with dense collagen andcalcium deposits which represents the hardened CTO body typical of thiscondition. The inner portion of a CTO body is softer than the distal andproximal ends which are the hardest part of a CTO body. A reduction invessel diameter is referred to as shrinkage or negative remolding. Thedistal and proximal ends of a CTO are often referred to as the fibrouscaps and are considered the hardest and most dense portions of a CTO.

In attempting to repair CTOs, the ability to complete a successfulrecanalization of a total occlusion is limited as surgeons have haddifficulty crossing the CTO with a guidewire. The inability to cross aCTO with a guidewire is the principal cause of failure of the procedureto remove such blockage, as more than 50% fail for this reason.Traditional repair of a CTO proceeds through four distinct steps. First,the CTO is perforated. It is preferred that both the proximal and distalfibrous caps are perforated. Second, the lesion which gave rise to theplaque formation and ultimate CTO is debulked. Third, the blood vesselis dilated. And finally, given the high rate of reocclusion, therepaired or recanalized vessel is assisted in remaining a passablevessel by a supporting device, such as a stent.

There is a need in the industry for improved devices and methods toassist surgeons in crossing CTOs.

SUMMARY OF THE INVENTION

The present invention provides an improved medical catheter device andmethod for traversing an occlusion in a vessel. The device includes astraightening sleeve positioned at a distal aspect of a catheter, asteering sleeve having an arcuate distal end, and a guidewire slidablethrough the lumen of the steering sleeve. The steering sleeve has afirst position in which the arcuate distal end is straightened withinthe straightening sleeve, and a second position in which the steeringsleeve extends distally past the straightening sleeve to expose thearcuate distal end. The steering sleeve and straightening sleeve aresufficiently flexible without the guidewire positioned in the steeringsleeve that they can pass through tortuous anatomy during a surgicalprocedure. The guidewire can then be inserted in the steering sleeveafter the steering sleeve and straightening sleeve reach their desiredposition near the occlusion. The tip of the arcuate distal end of thesteering sleeve or the tip of the guidewire can be used to pierce theocclusion.

The present invention also provides an arrangement of hub assemblieswith locking mechanisms and motion limiting structures to facilitateadjusting and locking the relative positions of the straighteningsleeve, the steering sleeve, and the guidewire. Detent mechanisms areassociated with the motion limiting structures for providing controlledincremental movement of the sleeves and the guidewire.

According to a broad aspect of the present invention, a medical deviceis provided for traversing an occlusion in a vessel, comprising: astraightening sleeve positioned at a distal aspect of a catheter; asteering sleeve having an arcuate distal end, the steering sleeve andthe straightening sleeve being slidably moveable relative to each othersuch that in a first position the arcuate distal end of the steeringsleeve is straightened within the straightening sleeve and in a secondposition the steering sleeve extends distally past the straighteningsleeve to expose the arcuate distal end; and a guidewire disposedthrough the steering sleeve within the straightening sleeve.

According to another broad aspect of the present invention, an improvedarrangement of hub assemblies for a medical device is provided,comprising: a first hub assembly attached to an outer sleeve of acatheter; a second hub assembly attached to an inner sleeve of thecatheter; a first locking mechanism associated with the first hubassembly, the first locking mechanism being movable between a lockedcondition in which the outer and inner sleeves are locked together, andan unlocked condition in which the outer and inner sleeves are moveablerelative to each other; and a second locking mechanism associated withthe second hub assembly, the second locking mechanism being movablebetween a locked condition in which the inner sleeve is locked togetherwith a guidewire, and an unlocked condition in which the inner sleeveand the guidewire are moveable relative to each other.

According to yet another broad aspect of the present invention, a methodof traversing an occlusion in a vessel is provided, comprising the stepsof: providing a catheter having a straightening sleeve and a steeringsleeve which are slidably moveable relative to each other such that in afirst position a distal end of the steering sleeve with a presetcurvature at its distal end is straightened within the straighteningsleeve and in a second position the steering sleeve extends distallypast the straightening sleeve to expose at least a portion of the curveddistal end; inserting the catheter into a patient's body to a deploymentposition while maintaining the distal end of the steering sleevestraightened within the straightening sleeve; inserting a guidewirehaving a normally straight configuration through a lumen of the steeringsleeve after the catheter has been inserted to its deployment position;sliding the steering sleeve from its first position to its secondposition at the deployment position; and using the steering sleeve andthe guidewire positioned within the curved distal end of the steeringsleeve to traverse the occlusion.

Numerous other objects and features of the present invention will beapparent to those skilled in this art from the following descriptionwherein there is shown and described exemplary embodiments of thepresent invention, simply by way of illustration of the modes bestsuited to carry out the invention. As will be realized, the invention iscapable of other different embodiments, and its several details arecapable of modification in various obvious aspects without departingfrom the invention. Accordingly, the drawings and description should beregarded as illustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more clearly appreciated as thedisclosure of the present invention is made with reference to theaccompanying drawings. In the drawings:

FIG. 1 is a side view of a guidewire having a normally straightconfiguration for use with the present invention.

FIG. 2 is a side view of a precurved steering sleeve having a presetcurve for use with the present invention.

FIG. 3 is a side view of the precurved steering sleeve of FIG. 2 withthe guidewire of FIG. 1 positioned in the lumen thereof, showing how thenormally straight guidewire can be used to change the curvature of thesteering sleeve.

FIG. 4 is a side view showing the steering sleeve and guidewirepositioned within a straightening sleeve.

FIG. 5 shows a device of the present invention with the steering sleeveand guidewire positioned proximal to a CTO body which is to betraversed.

FIG. 6 shows a device of the present invention after the steering sleeveand guidewire have penetrated the proximal fibrous cap of the CTO bodyand are being repositioned within the CTO body to facilitate penetrationof the distal fibrous cap.

FIG. 7 shows a device of the present invention with an inflatableballoon positioned around the straightening sleeve to anchor the devicein a desired position with the vessel.

FIG. 8 is a side view of the straightening sleeve of the presentinvention showing regions of varied stiffness along the length of thestraightening sleeve.

FIG. 9 is a side view of the precurved steering sleeve of the presentinvention showing regions of varied stiffness along the length of thesteering sleeve.

FIG. 10 is a cross section view of a first hub configuration used tofacilitate the relative positioning and locking of the proximal ends ofthe guidewire, steering sleeve and straightening sleeve of the presentinvention.

FIG. 11 is a cross section view of a second hub configuration used tofacilitate the relative positioning and locking of the proximal ends ofthe guidewire, steering sleeve and straightening sleeve of the presentinvention.

FIG. 12 is a cross section view of a hub configuration with a guide tubeaccording to the present invention.

FIG. 13 is a perspective view of a guide tube having a splitconstruction for use with the hub configuration shown in FIG. 12.

FIG. 14 is a perspective view of a guide tube having a moldedconstruction for use with the hub configuration shown in FIG. 12.

FIG. 15 is a perspective view of an assembly of guide tubes that can besnapped over the sleeves and used with the hub configuration of thepresent invention.

FIG. 16 is a cross section view of a hub configuration with nestingcomponents.

FIG. 17 is a perspective view of a the hub configuration shown in FIG.16.

DETAILED DESCRIPTION OF THE INVENTION

A medical catheter device, hub assemblies and method according toembodiments of the present invention will now be described in detailwith reference to FIGS. 1 to 17 of the accompanying drawings.

A medical catheter device 10 for traversing a CTO 11 in a vessel 12according to the present invention includes a straightening sleeve 13, asteering sleeve 14, and a guidewire 15. As shown in FIG. 1, theguidewire 15 has a normally straight configuration. The guidewire 15 maybe any guidewire 15 used in catheter-based procedures and may have ablunt or sharpened shape at its distal tip 16. The shape of the distaltip 16 will depend on the particular application and the preference ofthe treating physician. The guidewire 15 can be made of surgical steelor any other suitable material known to one of skill in the art. Theguidewire 15 can be sized in the range of 5 to 20 mils (0.005″ to0.020″), and preferably in the range of about 10 to 16 mils (0.010″ to0.016″).

As shown in FIG. 2, the steering sleeve 14 has a preset curvature at itsdistal end 17 giving it an arcuate shape with a radius of curvature R1.The steering sleeve 14 is also sometimes referred to as a J-tippedneedle, J-needle, or needle sheath, and can be comprised of stainlesssteel, nitinol, superelastic alloys, plastic, polymer, or any othermaterial known to one of skill in the art to be rendered flexible. Thesteering sleeve 14 has a shape that is arcuate at its distal end 17 yetis elastic enough and has high enough curve retention properties to bestraightened without permanent deformation. The steering sleeve 14 canbe covered with a protective coating, such as PTFE or other fluorinatedmaterial.

The steering sleeve 14 can be made, for example, using the non-extrusionmethod for catheter manufacture described in U.S. Pat. No. 6,030,371. Ahard plastic, such as a high temperature thermoplastic called PEEK(poly-ether-ether-keytone), can be used as a liner for the steeringsleeve 14. A wire reinforcement and powder overcoat for the steeringsleeve 14 can be terminated a distance (e.g., one inch) from the distaltip 18 of the steering sleeve 14. This results in a steering sleeve 14that looks like a normal micro catheter, but has a smaller diameter,relatively strong extension at its distal end 17. This extension canthen be tipped by curving and/or machining. The distal tip 18 of thesteering sleeve 14 can be machined into a blunt tip, needle tip, pointedtip or crown cur. The hard plastic of the liner used to form the distalend 17 will allow the tip shape or cut to be maintained during thesurgical procedure. The distal end 17 can be curved to form the presetcurvature of the steering sleeve 14 without the influence of theovercoat of powder and reinforcements.

The preset curve in the distal end 17 of the steering sleeve 14 can beset so that it is in the proper shape/orientation as it exits thestraightening sleeve 13, or it can be over curved (i.e., preset with acurvature greater than what will be used during the surgical procedure).The over curvature can then be altered using the guidewire 15 during thesurgical procedure, as explained below.

As shown in FIG. 3, the guidewire 15 is slidably disposed in the lumenof the steering sleeve 14 and is moveable along the long axis of thesteering sleeve 14. In this condition, the normally straightconfiguration of the guidewire 15 imparts a mild straightening force tothe arcuate distal end 17 of the steering sleeve 14 giving it a newradius of curvature R2 and reducing the amount of its deflection off thelong axis of the device 10. To compensate for this straightening force,the steering sleeve 14 can be manufactured with an over curve so thatwhen the guidewire 15 is passed through the steering sleeve 14, thecombination of over curve and the straight guidewire 15 results in theproper curve/orientation when the steering sleeve 14 exits thestraightening sleeve 13. This allows the use of a much stiffer guidewire15, which can improve the performance of the device 10 during thesurgical procedure.

As shown in FIG. 4, the straightening sleeve 13 has a normally straightconfiguration and functions to straighten the arcuate distal end 17 ofthe steering sleeve 14 when it is positioned within the straighteningsleeve 13. The straightening sleeve 13 is such that the steering sleeve14 is slidably moveable along the long axis and within a lumen of thestraightening sleeve 13. The straightening sleeve 13 can be comprised ofstainless steel, nitinol, plastic, polymer, or any other material knownto one or skill in the art to be rendered flexible.

The steering sleeve 14 has a first position, as shown in FIG. 4, inwhich the distal end 17 is straightened within the straightening sleeve13. The steering sleeve 14 is elastic enough that it is not permanentlydeformed when it is straightened within the straightening sleeve 13. Thesteering sleeve 14 has a second position, as depicted in FIGS. 5 to 7,in which the distal end 17 extends distally past the straighteningsleeve 13 to expose the preset curvature of the steering sleeve 14 tofacilitate steering of the device 10 during a surgical procedure. Theamount of curvature of the steering sleeve 14 during the surgicalprocedure is dependent upon the amount the steering sleeve 14 is exposedfrom the straightening sleeve 13 and whether the guidewire 15 ispositioned within the steering sleeve 14. In the second position, thetip 18 of the arcuate distal end 17 of the steering sleeve 14 or thedistal tip 16 of the guidewire 15 can be used for piercing, traversingand treating a CTO.

FIG. 5 shows the catheter device 10 of the present invention just priorto the penetration of a CTO body 11 by the guidewire 15. The CTO body 11is within a blood vessel 12 having an inner wall 19. On the inner wall19 is a plaque 20 which caused the formation of the CTO body 11completely blocking the lumen of the vessel 12. The CTO body 11 includesa proximal fibrous cap 21, a distal fibrous cap 22, and an inner coreregion 23. The fibrous caps 21, 22 are typically tough and comprisedmainly of hardened fibrous material. The inner core region 23 typicallybegins as soft plaque and is replaced by fibrous material. FIG. 5 showsthe catheter device 10 deployed to a position near the proximal fibrouscap 21 of the CTO body 11 with the distal end 17 of the steering sleeve14 extending from the straightening sleeve 13.

As shown in FIG. 7, a balloon 24 can be provided with the catheterdevice 10, which when inflated fits snugly within the inner wall 19 ofthe vessel 12. The balloon 24 functions to position and hold thestraightening sleeve 13 near the CTO body 11. The straightening sleeve13 extends beyond the balloon 24.

The steering sleeve 14 can then be used to align the appropriate“attack” angle for using the guidewire 15 to penetrate the proximalfibrous cap 21. The guidewire 15 can be advanced from the steeringsleeve 14 through the proximal cap 21 and into the inner core region 23.Alternatively, the steering sleeve 14 itself can be used to penetratethe proximal cap 21 to allow the guidewire 15 to advance through theinner core region 23.

The guidewire 15 and steering sleeve 14 can move independently of oneanother. For example, in FIG. 6 the steering sleeve 14 is repositionedwithin the CTO body 11, and specifically within the inner core region23, to facilitate aligning the guidewire 15 and ultimately theguidewire's penetration of the distal fibrous cap 22. The steeringsleeve 14 can be moved to its position within the inner core region 23via sliding movement over the guidewire 15 after the guidewire 15traverses the inner core region 23 and abuts the distal fibrous cap 22.

As shown in FIG. 8, the straightening sleeve 13 can have three regionsof varied stiffness, including a rigid region 25 at the distal end, aflexible region 26 proximal to the distal end, and a semi-flexibleregion 27 proximal to the flexible region 26. The regions 25-27 ofvaried stiffness can range in length depending upon the application. Forexample, the rigid region 25 can be between 0.5 and 50 mm in length, andpreferably between 1.0 and 10 mm. The flexible region 26 can be between10 and 1000 mm in length, and preferably between 20 and 800 mm. Thesemi-flexible region 27 can be of any length desired by the treatingphysician.

As shown in FIG. 9, the steering sleeve 14 can also have three regionsof varied stiffness, including a rigid region 28 at the distal end, aflexible region 29 proximal to the distal end, and a semi-flexibleregion 30 proximal to the flexible region 29. The regions of variedstiffness of the steering sleeve 14 can range in length depending uponthe application. For example, the rigid region 28 of the steering sleeve14 can be between 0.5 and 50 mm in length, and preferably between about1.0 and 15 mm. The flexible region 29 of the steering sleeve 14 can bebetween 10 and 1000 mm in length, and preferably between about 20 and800 mm. The semi-flexible region 30 can be of any length desired by thetreating physician.

A novel method for using the catheter device 10 according to the presentinvention will now be described. As explained above, the steering sleeve14 will contain an over bent curve at its distal end 17. The steeringsleeve 14 is inserted into the straightening sleeve 13 until it is justready to exit the straightening sleeve 13, and the guidewire 15 is notyet inserted into the steering sleeve 14. The catheter device 10 is thenadvanced into the patient's body to the treatment point. Since theguidewire 15 is not inserted at this point, the catheter device 10 willbe relatively floppy and will pass tortuous anatomy fairly easy. Once inthe proper position, the guidewire 15 is then inserted all the way tothe distal tip 18 of the steering sleeve 14. The guidewire 15 andsteering sleeve 14 are then pushed out of the straightening sleeve 13and the combination of the over curve and the straightening force of theguidewire 15 will result in a properly shaped curve. The guidewire 15can then be advanced out of the steering sleeve 14 to perforate theproximal cap 21 of the CTO 11. The guidewire 15 will extend generally ina straight line out of the steering sleeve 14 because only the steeringsleeve 14 is curved.

Improved hub assemblies for use with the catheter device described abovewill now be explained with reference to FIGS. 10 to 17. The hubassemblies can be used to give the treating physician the ability tomanipulate and lock the straightening sleeve 13, steering sleeve 14, andguidewire 15 together in any combination so that the components remainin the same relative position to one another and/or advanced together.

FIG. 10 shows a first hub assembly 35 attached to an outer sleeve 36(e.g., the straightening sleeve) of the catheter, and a second hubassembly 37 attached to an inner sleeve 38 (e.g., the steering sleeve).A first locking mechanism 39 is associated with the first hub assembly35. The first locking mechanism 39 is movable between a locked conditionin which the outer and inner sleeves 36, 38 are locked together, and anunlocked condition in which the outer and inner sleeves 36, 38 aremoveable relative to each other. The first locking mechanism 39 can be amechanical lock, such as a conventional compression or friction lock.

A first motion limiting structure 40 is attached to the first hubassembly 35 for limiting a range of relative linear movement between theouter sleeve 36 and the inner sleeve 38 when the first locking mechanism39 is in its unlocked condition. The first motion limiting structure 40includes a first tubular segment 41 having a threaded female coupler 42at one end and a raised flange 43 at the other end. The threaded femalecoupler 42 is connected to a corresponding threaded male coupler 44 onthe proximal side of the first hub assembly 35. The end of the firsttubular segment 41 with the raised flange 43 is slidably containedwithin a corresponding structure 45 on the distal side of the second hubassembly 37. When the threaded coupler 42 of the first tubular segment41 is fastened to the first hub assembly 35, the first and second hubassemblies 35, 37 are effectively connected together by the first motionlimiting structure 40. In this condition, the second hub assembly 37 isallowed to rotate and move linearly relative to the first tubularsegment 41, and hence relative to the first hub assembly 35, within thelimited range allowed by the opposing surfaces 46, 47 of the second hubassembly 37 that engage the raised flange 43 of the first tubularsegment 41. The outer and inner sleeves 36, 38 can still be lockedtogether against any relative movement using the first locking mechanism39. A detent mechanism 48 can be included in the first motion limitingstructure 40 for providing controlled incremental movement between theouter and inner sleeves 36, 38.

A second locking mechanism 49 is associated with the second hub assembly37. The second locking mechanism 49 is movable between a lockedcondition in which the inner sleeve 38 is locked together with theguidewire 15, and an unlocked condition in which the inner sleeve 38 andthe guidewire 15 are movable relative to each other. The second lockingmechanism 49 can have a construction similar to the first lockingmechanism 39, such as a conventional compression or friction lock.

A second motion limiting structure 50 is attached to the second hubassembly 37 for limiting a range of relative linear movement between theinner sleeve 38 and the guidewire 15 when the second locking mechanism49 is in its unlocked condition. The second motion limiting structure 50is similar in construction to the first motion limiting structure 40described above. The second motion limiting structure 50 includes asecond tubular segment 51 having a threaded female coupler 52 at one endand a raised flange 53 at the other end. The threaded female coupler 52is connected to a corresponding threaded male coupler 54 on the proximalside of the second hub assembly 37. The end of the second tubularsegment 51 with the raised flange 53 is slidably contained within acorresponding structure 55 on the distal side of a third hub 56 or othersuitable structure connected to the guidewire 15. When the threadedcoupler 52 of the second tubular segment 51 is fastened to the secondhub assembly 37, the second hub assembly 37 and the third hub 56 areeffectively connected together by the second motion limiting structure50. In this condition, the third hub 56 is allowed to rotate and movelinearly relative to the second tubular segment 51, and hence relativeto the second hub assembly 37, within the limited range allowed by theopposing surfaces of the third hub 56 that engage the raised flange 53of the second tubular segment 51. The second locking mechanism 49 canstill be used to lock the inner sleeve 38 together with the guidewire15. A detent mechanism 57 can be included in the second motion limitingstructure 50 for providing controlled incremental movement between theinner sleeve 36 and the guidewire 15.

FIG. 11 shows another embodiment of hub assemblies which does notinclude motion limiting structures. In this embodiment, the first hubassembly 60 includes a first locking mechanism 61 for locking togetherthe inner and outer sleeves 62, 63, and the second hub assembly 64includes a second locking mechanism 65 for locking together the innersleeve 62 and the guidewire 66.

FIG. 12 shows another embodiment of hub assemblies in which a firstguide tube 70 extends from a proximal end of the first hub assembly 71,and a second guide tube 72 extends from a proximal end of an innersleeve or guidewire 73. The second guide tube 72 is slidably received inthe first guide tube 70 to aid in the handling of the device during use.The guide tubes 70, 72 can be either molded into the respective hubassemblies 71, 74, as depicted by the second guide tube 72 in FIG. 12,or attached as a separate sleeve using a threaded coupling 75 or othersuitable connection, as depicted by the first guide tube 70. FIG. 13shows a guide tube 76 having a split sidewall 77 to facilitateattachment as a separate component over the inner sleeve or theguidewire 73, and FIG. 14 shows a guide tube 78 having a central bore 79which can be molded as an integral unit with the hub assemblies 71, 74.

FIG. 15 shows an assembly of guide tubes 80, 81, 82 that can be snappedover the sleeves and the guidewire 83 and used with the hubconfigurations of the present invention. FIGS. 16 and 17 show additionaldetails of these guide tubes 80-82.

As shown in FIG. 15, a first guide tube 80 is connected to the first hubassembly and/or the outer sleeve, a second guide tube 81 is connected tothe second hub assembly and/or the inner sleeve, and a third guide tube82 is connected to the guidewire 83. The guidewire 83 has a head 84secured to its proximal end, which is received in a correspondingstructure 85 within the third guide tube 82. The third guide tube 82 isslidably received within the second guide tube 81, and the second guidetube 81 is slidably received within the first guide tube 80. The guidetubes 80-82 can be made using materials that will allow smooth andcontrollable sliding movement between the parts to aid the surgeon inslidably positioning the inner and outer sleeves and the guidewirerelative to each other.

While the invention has been described in connection with specificembodiments thereof, it is to be understood that this is by way ofillustration and not of limitation, and the scope of the appended claimsshould be construed as broadly as the prior art will permit.

1. A method of traversing an occlusion in a vessel, comprising the stepsof: providing a catheter having a straightening sleeve and a steeringsleeve which are slidably moveable relative to each other such that in afirst position a distal end of the steering sleeve with a presetcurvature at said distal end is straightened within the straighteningsleeve and in a second position the steering sleeve extends distallypast the straightening sleeve to expose at least a portion of the curveddistal end; inserting the catheter into a patient's body to a deploymentposition while maintaining the distal end of the steering sleevestraightened within the straightening sleeve; inserting a guidewirehaving a normally straight configuration through a lumen of the steeringsleeve after the catheter has been inserted to its deployment position;sliding the steering sleeve from its first position to its secondposition at the deployment position; using the steering sleeve and theguidewire positioned within the curved distal end of the steering sleeveto traverse the occlusion; using a first motion limiting structure tolimit a range of relative linear movement between said straighteningsleeve and said steering sleeve, said first motion limiting structurecomprising a first set of opposing surfaces that define respective endsof a path of linear movement between said straightening sleeve and saidsteering sleeve, said first motion limiting structure allowing relativelinear movement between said straightening sleeve and said steeringsleeve within a limited range defined by said first set of opposingsurfaces; and using a second motion limiting structure to limit a rangeof relative linear movement between said steering sleeve and saidguidewire, said second motion limiting structure comprising a second setof opposing surfaces that define respective ends of a path of linearmovement between said steering sleeve and said guidewire, said secondmotion limiting structure allowing relative linear movement between saidsteering sleeve and said guidewire within a limited range defined bysaid second set of opposing surfaces.
 2. The method of traversing anocclusion according to claim 1, wherein said guidewire is sufficientlystiff to be used for perforating an occlusion.
 3. The method oftraversing an occlusion according to claim 1, wherein an arcuate distalend of the steering sleeve has a pointed tip to facilitate piercing anocclusion.
 4. The method of traversing an occlusion according to claim1, wherein an arcuate distal end of the steering sleeve contains apreset curvature, and said guidewire has a preset straight configurationthat imparts a straightening force on said arcuate distal end whichreduces said preset curvature, said guidewire being sufficiently stiffto be used for perforating an occlusion.
 5. The method of traversing anocclusion according to claim 1, wherein said straightening sleeve hasregions of varying flexibility along its length, wherein said regions ofvarying flexibility include a relatively rigid distal region and arelatively flexible proximal region.
 6. The method of traversing anocclusion according to claim 1, wherein said steering sleeve has regionsof varying flexibility along its length, wherein said regions of varyingflexibility include a relatively rigid distal region and a relativelyflexible proximal region.
 7. The method of traversing an occlusionaccording to claim 1, wherein said steering sleeve comprises a J-tippedneedle with an arcuate shape at its distal end, and said steering sleevebeing elastic enough at its distal end to be straightened withoutpermanent deformation.
 8. The method of traversing an occlusionaccording to claim 1, further comprising using a distal tip of thesteering sleeve to pierce the occlusion.
 9. The method of traversing anocclusion according to claim 1, further comprising using a distal tip ofthe steering sleeve to perforate proximal and distal fibrous caps of theocclusion.
 10. The method of traversing an occlusion according to claim1, further comprising using a distal tip of the guidewire to pierce theocclusion.
 11. The method of traversing an occlusion according to claim1, further comprising using a distal tip of the guidewire to perforateproximal and distal fibrous caps of the occlusion.
 12. The method oftraversing an occlusion according to claim 1, further comprising using adistal tip of the guidewire or a distal tip of the steering sleeve toperforate proximal and distal fibrous caps of the occlusion.
 13. Themethod of traversing an occlusion according to claim 12, furthercomprising moving the guidewire and the steering sleeve independently ofone another while traversing the occlusion.
 14. The method of traversingan occlusion according to claim 13, further comprising repositioning adistal tip of the steering sleeve within an inner core region of theocclusion by sliding the steering sleeve over the guidewire after theguidewire traverses the inner core region.
 15. The method of traversingan occlusion according to claim 1, wherein the preset curvature at thedistal end of the steering sleeve comprises an over-curve so that whenthe guidewire is passed through the steering sleeve the combination ofthe over-curve and the straight guidewire results in a proper curve whenthe steering sleeve exits the straightening sleeve, thereby allowing useof a stiffer guidewire.
 16. The method of traversing an occlusionaccording to claim 1, further comprising using a first hub assembly tomove and lock the straightening sleeve and the steering sleeve relativeto each other, and using a second hub assembly to move and lock thesteering sleeve and the guidewire relative to each other.
 17. The methodof traversing an occlusion according to claim 1, further comprising:using a first hub assembly attached to said straightening sleeve toprovide a locked condition in which the straightening sleeve and thesteering sleeve are secured together and an unlocked condition in whichthe straightening sleeve and the steering sleeve are moveable in alinear direction relative to each other; said first motion limitingstructure attached to said first hub assembly; using a second hubassembly attached to said steering sleeve to provide a locked conditionin which the steering sleeve and the guidewire are secured together andan unlocked condition in which the steering sleeve and the guidewire aremoveable in a linear direction relative to each other; and said secondmotion limiting structure attached to said second hub assembly.